Polyurethane-based foam may be used in a wide variety of products including, for example, automotive crash pads, sound insulation, vibration dampening, carpet backing, bedding, upholstery, furniture, and packing materials. Polyurethanes may be formed by reacting an isocyanate with a polyol. Isocyanates, in turn, may be formed by various methods. For example, isocyanates may be formed by reacting an amine (e.g., amine, amine hydrochloride, carbamate salt, and/or urea) with phosgene either in a liquid phase in the presence of a solvent or in a vapor phase with solvent added during a quench/cooling stage. Phosgene may be removed from this product mixture to form an isocyanate-containing feed for subsequent distillation.
Distillation columns may be used to fractionate a feed mixture into some or all of its component parts. For example, a distillation column may be used to separate a two-component feed mixture into two product streams: an upper product stream from the top of the column containing the lighter stream and a lower product stream from the bottom of the column containing the heavier component. A distillation column may be configured to yield a side product stream to separate, for example, more complex feed mixtures. However, this side product stream may be contaminated with light or heavy components depending on its location on the column. For example, a side product stream may be contaminated by lateral mixing of the components within the column and/or volatiles passing the side outlet on their way to the top of the column.
Lateral mixing may be reduced or eliminated in a distillation column with a vertical partition that divides the column into separate feed and outlet sections. Problems with contamination may persist, for example, where a feed mixture contains higher levels of lighter components. Reducing this contamination may require additional columns and/or additional thermal input, which may undesirably increase capital and/or production costs.